Powder cleaning systems and methods

ABSTRACT

A powder cleaning system can include a fluidized bed reactor configured to retain powder and fluidize the powder to remove adsorbate and/or other contaminants from the powder, at least one inlet line, and one or more gas sources configured to be in selective fluid communication with the fluidized bed reactor via the at least one inlet line to selectively provide an inlet flow having one or more gases to the fluidized bed reactor to fluidize the powder with the one or more gases within the fluidized bed reactor. The system can include at least one outlet line in fluid communication with the fluidized bed reactor and configured to allow removal of outlet flow which comprises the adsorbate and/or other contaminants from the fluidized bed reactor.

BACKGROUND 1. Field

The present disclosure relates to powder, e.g., for additivemanufacturing.

2. Description of Related Art

For superalloys (e.g. Fe—Ni based, Ni based, and Co based), the relationbetween surface adsorbed species and mechanical properties (i.e. afterdensification) has been well documented. Significant effects of oxygenlevels on tensile, impact, and creep properties, etc. have beenreported. Oxygen at powder surfaces can contribute significantly to theweakening of interparticle boundaries. A prior particle boundary (PPB)issue has been observed during hot isostatic pressing (HIP) andselective laser melting (SLM) of IN718 superalloy.

The presence of highly stable surface oxides has been shown to havedetrimental effects on HIP and SLM. The PPB issue was shown to resultfrom surface contamination with pre-alloyed powder and oxide particlesformed along the PPB. The precipitates are very brittle, therebypotentially providing a fracture path. Thus, use of traditional powderresult in limits placed on consolidated products formed from the powder.Despite significant efforts to reduce the effects of PPB's, and therebyextend the life of related products (e.g., with aerospace applications),there is still no effective and reliable method to do so.

Such conventional methods and systems have generally been consideredsatisfactory for their intended purpose. However, there is still a needin the art for improved powder cleaning systems and methods. The presentdisclosure provides a solution for this need.

SUMMARY

A powder cleaning system can include a fluidized bed reactor configuredto retain powder and fluidize the powder to remove adsorbate and/orother contaminants from the powder, at least one inlet line, and one ormore gas sources configured to be in selective fluid communication withthe fluidized bed reactor via the at least one inlet line to selectivelyprovide an inlet flow having one or more gases to the fluidized bedreactor to fluidize the powder with the one or more gases within thefluidized bed reactor. The system can include at least one outlet linein fluid communication with the fluidized bed reactor and configured toallow removal of outlet flow which comprises the adsorbate and/or othercontaminants from the fluidized bed reactor.

The system can include a filter for capturing particles, the filterdisposed in the at least one outlet line. The system can include aliquid trap disposed downstream of the filter and configured to trapliquid entrained in the outlet flow. The liquid trap can include a ventfor venting gas of the outlet flow.

The inlet line can include at least one inlet line valve configured toselectively allow flow from the one or more gas sources to the fluidizedbed reactor. The system can include a bypass line configured to fluidlyconnect the inlet line and the liquid trap to allow at least some gas inthe inlet line to flow to the vent, wherein the bypass line includes abypass valve configured to selectively allow bypass flow.

The system can include a pressure release valve (PRV) disposed in theinlet line to allow bleeding of pressure above a threshold pressure. Thesystem can include a pressure sensor downstream of the PRV.

The at least one inlet line valve can be downstream of the pressuresensor. The one or more gas sources can each include a source valveand/or a mass flow controller (MFC) for controlling an amount and/orproportion of each gas in the inlet flow. The one or more gas sourcescan include at least one of an argon (Ar) source, an ammonia (NH₃)source, a nitrogen (N₂) source, a hydrogen (H₂) source or a helium (He)source.

The fluidized bed reactor can include an outer housing defining an outerspace and a powder container disposed within the outer space anddefining an inner space. The fluidized bed reactor can include a gasdistributor plate between the outer space and the inner space at thebottom of the powder container. The gas distributor plate can include aplurality of holes smaller than particles of the powder configured toprevent powder from falling through the plate and to allow the inlet gasto pass therethrough into the powder within the powder container tofluidize the powder. The inlet line can be in fluid communication withthe outer space and the outlet line is in fluid communication with theinner space such that inlet gas must flow through the gas distributorplate and the powder.

In certain embodiments, a temperature sensor can be disposed in thermalcommunication with the outer space to sense a temperature of the inletgas, and a temperature sensor in thermal communication with the outletline to sense a temperature of the outlet gas. In certain embodiments,the system can include a heater or cooler disposed in thermalcommunication with the inlet flow to control the temperature of theinlet flow.

A method for cleaning a powder can include fluidizing powder in afluidized bed reactor with an inlet gas to remove adsorbate and/or othercontaminants to produce cleaned powder. Fluidizing powder includesflowing gas through the powder in a direction opposite to gravity. Theinlet gas can include at least one of argon (Ar), ammonia (NH₃),nitrogen (N₂), hydrogen (H₂), or helium (He). Fluidizing the powder canbe performed after at least one of powder production, powdercharacterization and/or testing, and/or powder processing. Fluidizingpowder can include controlling a temperature and/or pressure of theinlet gas as a function of one or more powder characteristics. Themethod can include sintering the cleaned powder to form an additivelymanufactured article.

These and other features of the systems and methods of the subjectdisclosure will become more readily apparent to those skilled in the artfrom the following detailed description taken in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject disclosureappertains will readily understand how to make and use the devices andmethods of the subject disclosure without undue experimentation,embodiments thereof will be described in detail herein below withreference to certain figures, wherein:

FIG. 1 is a schematic diagram of an embodiment of a system in accordancewith this disclosure, showing powder being fluidized; and

FIG. 2 is a flow diagram of an embodiment of a method in accordance withthis disclosure.

DETAILED DESCRIPTION

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectdisclosure. For purposes of explanation and illustration, and notlimitation, an illustrative view of an embodiment of a system inaccordance with the disclosure is shown in FIG. 1 and is designatedgenerally by reference character 100. Other embodiments and/or aspectsof this disclosure are shown in FIG. 2. The systems and methodsdescribed herein can be used to clean powder (e.g., removing moistureand oxygen adsorbed by the powder) used for additive manufacturing(e.g., alloy powder), for example, Selective Laser Melting (SLM), DirectMetal Laser Sintering (DMLS), Electron Beam Melting (EBM), etc.

Referring to FIG. 1, a powder cleaning system 100 can include afluidized bed reactor 101 configured to retain powder 103 and fluidizethe powder 103 to remove adsorbate (e.g., moisture, oxygen) and/or othercontaminants (e.g., dirt or other impurity) from the powder 103. Thesystem 100 can include one or more gas sources 105 configured to be inselective fluid communication with the fluidized bed reactor 101 via atleast one inlet line 107 to selectively provide an inlet flow 109 havingone or more gases to the fluidized bed reactor 101 to fluidize thepowder 103 with the one or more gases within the fluidized bed reactor101. The system 100 can include at least one outlet line 111 in fluidcommunication with the fluidized bed reactor 101 which can be configuredto allow removal of outlet flow 113 which comprises the adsorbate and/orother contaminants from the fluidized bed reactor 101.

The system 100 can include a filter 115 for capturing particles, thefilter 115 disposed in the at least one outlet line 111. The system 100can include a liquid trap 117 disposed downstream of the filter 115 andconfigured to trap liquid and/or powder entrained in the outlet flow113. The liquid trap 117 can include a vent 119 for venting gas of theoutlet flow 113, for example.

The inlet line 107 can include at least one inlet line valve 121configured to selectively allow flow from the one or more gas sources105 to the fluidized bed reactor 101. The system 100 can include abypass line 123 configured to fluidly connect the inlet line 107 and theliquid trap 117 to allow at least some gas in the inlet line 107 to flowto the vent 119. The bypass line 123 can include a bypass valve 125configured to selectively allow bypass flow. In certain embodiments, thebypass line 123 and bypass valve 125 can be utilized to prevent pressurespikes in the fluidized bed reactor 101. In certain embodiments, thebypass valve 125 and the inlet line valve 121 can be a single three wayvalve to select between open, closed, or bypass, or to regulate betweenopen and bypass states in any suitable manner.

The system 100 can include a pressure release valve (PRV) 127 disposedin the inlet line 107 (e.g., downstream of the bypass line 123) andconfigured to allow bleeding of pressure above a threshold pressure. ThePRV 127 can be or include a check valve, for example, or any othersuitable valve (e.g., to actuate a threshold pressure to avoidoverpressure of the reactor 101). The system 100 can include a pressuresensor 129 downstream of the PRV 127, for example, or in any othersuitable location in the inlet line 127.

The at least one inlet line valve 121 can be downstream of the pressuresensor 129. The one or more gas sources 105 can each include a sourcevalve 131 and/or a mass flow controller (MFC) 133 for controlling anamount and/or proportion of each gas in the inlet flow 109. The one ormore gas sources 105 can include at least one of an argon (Ar) source,an ammonia (NH₃) source, a nitrogen (N₂) source, a hydrogen (H₂) source,or a helium (He) source, or any combination thereof, e.g., as shown.

The fluidized bed reactor 101 can include an outer housing 101 adefining an outer space 101 b and a powder container 101 c disposedwithin the outer space 101 b and defining an inner space 101 d. Thefluidized bed reactor 101 can include a gas distributor plate 101 ebetween the outer space 101 b and the inner space 101 d at a bottom ofthe powder container 101 c as shown. The gas distributor plate 101 e caninclude a plurality of holes smaller than particles of the powder 103configured to prevent powder 103 from falling through the plate 101 eand to allow the inlet gas 109 to pass therethrough into the inner space101 d to fluidize the powder 103 within the powder container 101 c. Asshown, the inlet line 107 can be in fluid communication with the outerspace 101 b and the outlet line 111 can be in fluid communication withthe inner space 101 d such that inlet gas 109 must flow through the gasdistributor plate 101 e and the powder 103.

In certain embodiments, a temperature sensor 135 can be disposed inthermal communication with the outer space 101 b to sense a temperatureof the inlet gas 109, and a temperature sensor 135 can be disposed inthermal communication with the outlet line 111 to sense a temperature ofthe outlet gas 113. In certain embodiments, the system 100 can include aheater or cooler disposed in thermal communication with the inlet flow109 (e.g., in inlet line 107) to control a temperature of the inlet flow109.

In certain embodiments, the system can include a controller (not shown)operatively connected to each of the valves 121, 125, 131 and/or sensors129, 135 to control a state of the system 100. The controller caninclude any suitable software and/or hardware modules to perform anysuitable function, e.g., those disclosed herein. For example, at startup, the controller can open the bypass valve 125 before or while openingone or more of the source valves 131 and/or inlet line valve 121 toprevent a pressure spike in the fluidization bed reactor 101. Thecontroller can close the bypass valve 125 after steady state operationis reached either completely and/or partially to regulate pressure tothe fluidization bed reactor 101. Any valve disclosed herein can be ashut off valve or a pressure regulating valve, or any other suitablevalve. For example, inlet line valve 121 can be configured to regulatepressure.

The controller can be operatively connected to a heater or cooler tocontrol the temperature of the inlet gas. In certain embodiments, thecontroller can include settings configured to provide a certainpressure, gas mixture or type, and temperature to the inlet flow 109based on one or more powder characteristics (e.g., powder type, particlesize, powder chemistry, amount of powder).

Referring to FIG. 2, a method 200 for cleaning a powder can includefluidizing powder in a fluidized bed reactor with an inlet gas to removeadsorbate and/or other contaminants to produce cleaned powder.Fluidizing powder includes flowing gas through the powder in a directionopposite to gravity. The inlet gas can include at least one of argon(Ar), ammonia (NH₃), nitrogen (N₂), hydrogen (H₂), or helium (He).

As shown, fluidizing the powder can be performed after at least one ofpowder production, powder characterization and/or testing, and/or powderprocessing. Fluidizing powder can include controlling a temperatureand/or pressure and/or a gas composition of the inlet gas as a functionof one or more powder characteristics. The method can include sinteringthe cleaned powder to form an additively manufactured article.

In certain embodiments, argon, nitrogen, and/or helium can be used forremoving oxygen and moisture adsorbed by the powder, and ammonia,hydrogen, and/or nitrogen can be used to treat powder after removal ofthe adsorbed oxygen and moisture. Any single gas and/or any combination(e.g., diluted ammonia) can be used.

Certain embodiments can utilize a fluidized bed reactor to displaceundesirable adsorbed species (i.e. oxygen, moisture, etc.) on superalloypowder surfaces, for example. Embodiments of the reactor techniqueinvolve suspending solid particles by upward fluid flow. Rapid heat andmass transfer between the gas and solid particles can provide analternative approach to other powder treatment methods. The treatmentconditions (i.e. fluidization velocity, temperature, time, gascompositions, etc.) can be determined on a case-by-case basis accordingto the superalloy powder properties (e.g. particle diameter, density,etc.), surface oxygen contamination, and desired level of oxygenremoval. Embodiments provide a flexible, economically feasible, andscalable method of uniform particle mixing and temperature gradients.Embodiments can remove surface oxygen without affecting bulk structureor morphology.

In certain embodiments, the first step in powder metallurgy (PM)processes can be the fabrication of metal powders. Removal of surfaceoxygen by fluidized bed gas reaction can be implemented at a severalstages during the fabrication process as well as along the pathway ofgenerating a finished part. Example processes used in powder productioninclude solid-state reduction, atomization, electrolysis, and chemical.

In solid-state reduction, an ore material is first crushed (usuallymixed with carbon), and passed through a furnace whereby the carbon andoxygen are reduced from the powder leaving behind a compacted spongemetal which crushed, separated from all non-metallic material, andsieved.

In the atomization process, molten metal is separated into smalldroplets and frozen rapidly before the drops come into contact with eachother or with a solid surface. The technique is applicable to all metalsthat can be melted.

Electrolysis is carried out by selecting conditions, such as electrolytecomposition and concentration, temperature, and current density, manymetals current density whereby metals are deposited in a spongy orpowdery state. Subsequent processing such as washing, drying, reducing,annealing, and crushing is often required to produce high-purity andhigh-density powders. However, due to high energy costs, this process istypically limited to high-value powders.

The chemical method is the most common whereby chemical powdertreatments involve oxide reduction, precipitation from solutions, andthermal decomposition. The powders produced can have a great variationin properties and yet have closely controlled particle size and shape.

Embodiments can be used as post-processing stage associated with any ofthe processes mentioned above, for example, to generate lowoxygen/moisture surfaces. Embodiments can be used at any other suitablepoint, e.g., before sintering of the powder.

As will be appreciated by those skilled in the art, aspects of thepresent disclosure may be embodied as a system, method, or computerprogram product. Accordingly, aspects of this disclosure may take theform of an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.), or anembodiment combining software and hardware aspects, all possibilities ofwhich can be referred to herein as a “circuit,” “module,” or “system.” A“circuit,” “module,” or “system” can include one or more portions of oneor more separate physical hardware and/or software components that cantogether perform the disclosed function of the “circuit,” “module,” or“system”, or a “circuit,” “module,” or “system” can be a singleself-contained unit (e.g., of hardware and/or software). Furthermore,aspects of this disclosure may take the form of a computer programproduct embodied in one or more computer readable medium(s) havingcomputer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thisdisclosure may be written in any combination of one or more programminglanguages, including an object oriented programming language such asJava, Smalltalk, C++ or the like and conventional procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The program code may execute entirely on the user's computer,partly on the user's computer, as a stand-alone software package, partlyon the user's computer and partly on a remote computer or entirely onthe remote computer or server. In the latter scenario, the remotecomputer may be connected to the user's computer through any type ofnetwork, including a local area network (LAN) or a wide area network(WAN), or the connection may be made to an external computer (forexample, through the Internet using an Internet Service Provider).

Aspects of the this disclosure may be described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of thisdisclosure. It will be understood that each block of any flowchartillustrations and/or block diagrams, and combinations of blocks in anyflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inany flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified herein.

Those having ordinary skill in the art understand that any numericalvalues disclosed herein can be exact values or can be values within arange. Further, any terms of approximation (e.g., “about”,“approximately”, “around”) used in this disclosure can mean the statedvalue within a range. For example, in certain embodiments, the range canbe within (plus or minus) 20%, or within 10%, or within 5%, or within2%, or within any other suitable percentage or number as appreciated bythose having ordinary skill in the art (e.g., for known tolerance limitsor error ranges).

Any suitable combination(s) of any disclosed embodiments and/or anysuitable portion(s) thereof are contemplated herein as appreciated bythose having ordinary skill in the art.

The embodiments of the present disclosure, as described above and shownin the drawings, provide for improvement in the art to which theypertain. While the subject disclosure includes reference to certainembodiments, those skilled in the art will readily appreciate thatchanges and/or modifications may be made thereto without departing fromthe spirit and scope of the subject disclosure.

What is claimed is:
 1. A powder cleaning system, comprising: a fluidizedbed reactor configured to retain powder and fluidize the powder toremove adsorbate and/or other contaminants from the powder; at least oneinlet line; one or more gas sources configured to be in selective fluidcommunication with the fluidized bed reactor via the at least one inletline to selectively provide an inlet flow having one or more gases tothe fluidized bed reactor to fluidize the powder with the one or moregases within the fluidized bed reactor; at least one outlet line influid communication with the fluidized bed reactor and configured toallow removal of outlet flow which comprises the adsorbate and/or othercontaminants from the fluidized bed reactor; a bypass line configured tofluidly connect the inlet line and the liquid trap to allow at leastsome gas in the inlet line to flow to the vent, wherein the bypass lineincludes a bypass valve configured to selectively allow bypass flow; andpressure release valve (PRV) disposed in the inlet line to allowbleeding of pressure above a threshold pressure, wherein the PRV isdownstream of the bypass line.
 2. The system of claim 1, furthercomprising a filter for capturing particles, the filter disposed in theat least one outlet line.
 3. The system of claim 2, further comprising aliquid trap disposed downstream of the filter and configured to trapliquid entrained in the outlet flow.
 4. The system of claim 3, whereinthe liquid trap includes a vent for venting gas of the outlet flow. 5.The system of claim 4, wherein the inlet line includes at least oneinlet line valve configured to selectively allow flow from the one ormore gas sources to the fluidized bed reactor.
 6. The system of claim 1,further comprising a pressure sensor downstream of the PRV.
 7. Thesystem of claim 6, wherein the at least one inlet line valve isdownstream of the pressure sensor.
 8. The system of claim 7, wherein theone or more gas sources each include a source valve and a mass flowcontroller (MFC) for controlling an amount and/or proportion of each gasin the inlet flow.
 9. The system of claim 8, wherein the one or more gassources can include at least one of an argon (Ar) source, an ammonia(NH₃) source, a nitrogen (N₂) source, a hydrogen (H₂) source or a helium(He) source.
 10. The system of claim 1, wherein the fluidized bedreactor includes an outer housing defining an outer space and a powdercontainer disposed within the outer space and defining an inner space.11. The powder container of claim 10, further comprising a gasdistributor plate between the outer space and the inner space at abottom of the powder container, wherein the gas distributor plateincludes a plurality of holes smaller than particles of the powderconfigured to prevent powder from falling through the gas distributorplate and to allow the inlet gas to pass therethrough into the powderwithin the powder container to fluidize the powder, wherein the inletline is in fluid communication with the outer space and the outlet lineis in fluid communication with the inner space such that inlet gas mustflow through the gas distributor plate and fluidize the powder.
 12. Thesystem of claim 11, further comprising a temperature sensor disposed inthermal communication with the outer space to sense a temperature of theinlet gas, and a temperature sensor in thermal communication with theoutlet line to sense a temperature of the outlet gas.